spokewrench

So I scheduled my 1st service and the tech is telling me GM won’t pay for or recommends a trans flush ? I’ve heard that this is supposed to be done ?

dragnz90

There is no flush required, just oil change with filter, and change the transmission filter before 7,500 miles

JerryU

Nope! Spent 2 hours with great Corvette tech who did my engine oil/filter change as well as did the flush AS REQUIRED AS PART OF THE DCT FILTER CHANGE. Tech showed me the GM procedure on the GM service computer that said run the flush BEFORE removing DCT filter as it send any material in valves and passages to the filter before removing!

Here is pic of his PC connected to my OBD port and GM's computer via WiFi. The GM computer managed the whole process with the engine running. Took about 10 minutes and I watched the screen.

BIG Dave

Seems to be conflicting information on this. According to Post #9 in this thread, the flush is for DCT’s that are experiencing problems and/or throwing codes. It would be great if GM would clarify this once and for all!

https://www.corvetteforum.com/forums...post1603588301

RKCRLR

Ask the dealer to show you the DCT filter replacement procedure. The procedure that is brought up on the computer screen and the tech is supposed to follow. See if the first step is to perform the flush procedure.

Keep in mind this is an internal flush procedure and the fluid does not get replaced.

MikeinAZ

that change includes a flush and it's free. It doesn't swap fluid out but is a procedure that flushes the solenoids and traps any particulates in the filter before removing it.

JerryU

^^^
Yep a DCT flush is required BEFORE DCT filter is changed. I recall the Tech's GM Service Procedure Computer screen said why (i.e. to get any debris into the filter before it was changed etc.)

I also had my DCT filter changed when I had my engine oil changed at ~12 months with 5% life showing. I had less than 4000 miles on my C8. The main reason was enough folks have had DCT CELs showing a flush was needed. Assume DCT clutch material does accumulate. In fact my clutches were a bit rough when stopped and crawling forward until I had about 1000 miles. After that they were very smooth as when crawling into the garage watching and carefully controlling the driver's mirror tip to wood door molding gap!

So I'll need no DCT filter change year 2 when I'll have about 7000 miles on the car and ~3500 on the new filter. BUT in year 3 I will require a complete DCT fluid change (per note 4 in the Maintenance Table See below.) Probably have the DCT Filter changed again at that time as well.

Bburr

Yep a DCT fluid change is required BEFORE DCT filter is changed. I recall the Tech's GM Service Procedure Computer screen said why (i.e. to get any debris into the filter before it was changed etc.)

Don't you guys ever read what you write. Not a "fluid change" but a FLUSH.
Also Year 3 doesn't require a fluid change per NOTE 4, but 45,000 miles.

JerryU

^^^
Only when I get paid like by CarTech etc! Pic is right! Read that. Glad you caught -Changed.

Read note 4, just like an engine oil change it says 45,000 miles OR 3 years whichever occurs 1st!

BIG Dave

Okay, let’s say the flush (not change) is required. What about most of the 2020’s that had their DCT canister filter change before the updated memo went out? Can they go back and get a flush? I’m guessing no?

JerryU

^^^
I'd guess NOT free. But I recall mid 2021 before I went in September 2021 with my 2020 this question of flush or not came up. I asked the tech who did mine. It was his 1st C8. He said because of that he reviewed both the GM procedure and Tremec info.

RKCRLR

It will be interesting to see if the flush procedure remains in the DCT filter replacement procedure for subsequent filter changes. We don't know exactly they incorporated the flush procedure. It could have been for diagnostics since they were requiring the filters to be returned to GM for evaluation. Perhaps they were just trying to find out what contaminants were remaining in the transmission after manufacturing and the flush was to capture the contaminates. Or perhaps once break-in has been completed the flush isn't necessary.

JerryU

^^^
At very slow speeds (<3 mph) I could 'feel' the 1st gear clutch slipping. After 500 or 1000 miles it's not noticeable. I crawl into my garage managing the gap from my extended driver mirror tip to the garage door wood molding. If I keep the gap ~2 inches or less it there is plenty of room from the passenger side mirror to door frame.

I also drove in Manual Mode for the 1st month and was pulling both paddles to disengage both clutches as I came to a stop. Now don't bother. Surly there was some clutch disk material collected and perhaps causing partial clogging of some small passages.

Assume that initial wear would not be repeated.

Andybump

So, still no available documentation confirming the performance of the "flush" as part of the first DCT filter change, right? The only place it can be seen is on the tech's computer, right? So, someone who has seen that, did it actually use the term "flush" in the first step? As I mentioned in another thread, I found a set of procedures in the Service Manual, all of which are called Transmission Service Cleaning Procedures, and also "Hydraulic Control System Cleaning Procedures. These procedures, in the 2020 manual, are called for in response to certain codes and related diagnostic test results. They are not called for in the section on DTC filter replacement. I suspect that they are the procedures that have been added to the filter change procedure in the tech's computer, but I do not know. Here is the list of those procedures from the manual.

RKCRLR

It is called "flush". The procedure is posted in post 9 of this thread:
https://www.corvetteforum.com/forums...post1603588301

mazurekd

Something I saved when this “flush thing” was first talked about. If my memory is correct it was RCKLR (?) that posted this.

RKCRLR

I may have reposted it but I just stole it from someone else

JerryU

^^^
Yep I got the pic I posted in #7 from the Forum. I also added that a complete 10.6 quart DCT fluid replacement is required at a maximum of 3 years.

BUT I looked at the tech's computer around September 1st 2021 when I had my 2020 engine oil changed as the OLM said 5% life left. Had the flush and filter changed as well with <4000 miles -all on GM's dime. Looked at tech's computer on his shop desk, which he showed me prior to doing the flush. As I recall it gave the reason which was to collect any debris in the filter for it was changed. Took ~10 minutes and the computer screen showed what was occurring as you could hear "things" going on in the trans the GM computer was controlling.

His was reading the dealer paid GM service info.

I'll need nothing for the DCT year 2 as I'll have ~7500 miles on the C8 and ~3500 on the new filter. BUT year 3 I'll have the fluid changed (as required) and probably a new filter installed.

bhvrdr

Flushes include the fluid change.

Did you read note 4? It says 3 years or the miles... whichever comes first.

JerryU

^^^^
The flush before a filter change just pulls possible debris in passages, valves, actuaries etc into the filer before it's change. Assume the GM computer program may have been using reverse flow. It took ~10 minutes and trans elements were

Only fluid added was the ~8oz to replace that lost with the filter and to get it to the fill level.